R. E. M. Hedges

Improvements to the Pretreatment of Bone at Oxford

Bone is one of the most widely used materials for dating archaeological activity. It is also relatively difficult to pretreat effectively and new methods are an area of active research. The purpose of the chemical pretreatment of bone is to remove contaminants present from burial and to do so in a way which does not add any additional laboratory contaminant. To some extent, these two aims must be balanced since, on the whole, the more complex the procedure and the more steps included, the greater the chance for contamination. At the Oxford Radiocarbon Accelerator Unit (ORAU), the method used is a continuous-flow or manual acid/base/acid (ABA) treatment followed by gelatinization and ultrafiltration (based on Brown et al. [1988]; documented in Bronk Ramsey et al. [2000]). We find this overall method is very effective at removing more recent contamination in old bones. However, two aspects of the method have recently been improved and are reported here: the redesign of ORAUs continuous flow pretreatment and a new protocol in our pretreatment ultrafiltration stage.

Investigations into the effect of diet on modern human hair isotopic values

Carbon and nitrogen isotopic analysis of body tissues is one of the few techniques that can furnish quantitative information about the diet of archaeological humans. The study of the effects of various diets on modern human isotopic values can help to refine palaeodietary theories, and such work also enables the testing of palaeodietary theories independent of archaeological remains and interpretations. This report discusses the use of modern human hair as a sample material for isotopic analysis. The biogenic carbon and nitrogen isotopic signal is well preserved in hair, and the isotopic values of the keratin can be related to diet. We show that atmospheric and cosmetic contamination of hair keratin does not appear to affect the measured isotopic values. In a small study of Oxford residents, we demonstrate that the magnitude of the nitrogen isotopic values of hair keratin reflects the proportion of animal protein consumed in the diet: omnivores and ovo-lacto-vegetarians have higher delta15N than vegans. There was an observed relationship between the reported amount of animal protein eaten (either meat or secondary animal products) and the nitrogen isotopic values within the two groups of omnivores and ovo-lacto-vegetarians, indicating that an increasing amount of animal protein in the diet results in an increase in the delta15N of hair keratin. This provides the first independent support for a long-held theory that, for individuals within a single population, a diet high in meat equates to elevated nitrogen isotopic values in the body relative to others eating less animal protein. The implications of such results for the magnitude of the trophic level effect are discussed. Results presented here also permit a consideration of the effects of a change of diet in the short and long term on hair keratin isotopic values.

New evidence of Lateglacial cereal cultivation at Abu Hureyra on the Euphrates

Hitherto, the earliest archaeological finds of domestic cereals in southwestern Asia have involved wheats and barleys dating from the beginning of the Holocene, 11–12000 calendar years ago. New evidence from the site of Abu Hureyra suggests that systematic cultivation of cereals in fact started well before the end of the Pleistocene by at least 13000 years ago, and that rye was among the first crops. The evidence also indicates that hunter-gatherers at Abu Hureyra first started cultivating crops in response to a steep decline in wild plants that had served as staple foods for at least the preceding four centuries. The decline in these wild staples is attributable to a sudden, dry, cold, climatic reversal equivalent to the ‘Younger Dryas’ period. At Abu Hureyra, therefore, it appears that the primary trigger for the occupants to start cultivating caloric staples was climate change. It is these beginnings of cultivation in the late Pleistocene that gave rise to the integrated grain-livestock Neolithic farming systems of the early Holocene.

A diffusion-adsorption model of uranium uptake by archaeological bone

Abstract An argument for the possibility of uranium uptake by buried bone taking place through the adsorption of uranyl species on bone mineral is advanced. In the light of this a diffusion-adsorption model for uranium uptake by buried bone is developed, the necessary constants are evaluated from the literature and from laboratory measurements of the partition coefficient between solution and bone mineral. The geochemical and hydrological parameters which control uptake are discussed. The predictions of the model are shown to be in general accordance with the timescale, magnitude, and distribution of uranium uptake in archaeological bone. Using the model, specific predictions of the variation of apparent uranium-series ages in bone can be made, and bone is shown clearly not to conform to the closed system assumption. When the model is extended to tooth enamel it is found to be incompatible with the early uptake model used for ESR dating, but to fall between the early uptake and linear uptake models. Similarly, it suggests that uranium-series dates on enamel assuming a closed system are liable to underestimate the true age by at least one-third.

A Review of Current Approaches in the Pretreatment of Bone for Radiocarbon Dating by AMS

Although the reliability of 14C dates of bone has increased greatly since AMS methods permitted better pretreatment on smaller samples, most old, badly contaminated or severely weathered bone still give serious problems. Several groups have recently proposed improvements to sample purification methods, often supported by a number of 14C measurements. We present here an overview of these improvements. The issue is complicated by the following: 1. Different problems are presented depending on age, preservation and degree of contamination of bone. 2. Methods may or may not be developed with routine application in mind. 3. Determining the conditions for which any method can be regarded as reliable is not at all straightforward.

A freshwater diet-derived 14C reservoir effect at the Stone Age sites in the Iron Gates gorge

Human bones from single inhumation burials and artifacts made from terrestrial mammal (ungulate) bone found in direct association with the skeletons were obtained from the Stone Age site of Schela Cladovei situated just below the Iron Gates Gorge of the River Danube. The results of stable isotope analyses of the human bone collagen are consistent with a heavy dependence on aquatic protein while radiocarbon dating of the samples reveals an offset of 300-500 years between the two sample types, indicating a freshwater reservoir effect in the human bone samples. Since protein consumption is by far the major source of nitrogen in the human diet we have assumed a linear relationship between delta (super 15) N and the level of aquatic protein in each individuals diet and derived a calibration for (super 14) C age offset versus delta (super 15) N which has been applied to a series of results from the site at Lepenski Vir within the gorge. The corrected (super 14) C ages (7310-6720 BP) are now consistent with the previous (super 14) C age measurements made on charcoal from related contexts (7360-6560 BP). In addition, the data indicate a change from a primarily aquatic to a mixed terrestrial/aquatic diet around 7100 BP and this may be argued as supporting a shift from Mesolithic to Neolithic. This study also has wider implications for the accurate dating of human bone samples when the possibility exists of an aquatic component in the dietary protein and strongly implies that delta (super 15) N analysis should be undertaken routinely when dating human bones.

Sulphur isotopic variation in ancient bone collagen from Europe: implications for human palaeodiet, residence mobility, and modern pollutant studies

We report here on the first measurements of δ34S in small (<10 mg) samples of ancient bone collagen extracted from humans (n=23) and animals (n=4) from various European archaeological sites. Measurement of δ34S values complement collagen δ13C and δ15N measurements and can provide corroboratory palaeodietary insights or new locality information. In areas where there are clear δ34S differences between marine, freshwater and terrestrial ecosystems they can be used to infer the consumption of foods from these systems. Also, as collagen δ34S values reflect local environment δ34S values, they can be used to identify the region where an individual normally resides, and therefore identify migratory individuals. Modern animal bone collagen δ34S values were also measured (n=7) and it was observed that such values may be confounded by modern sulphur pollutants, and we propose that archaeological material, which is free from modern sulphur pollutants, would provide appropriate baseline material for ecosystem studies.

U-series dating of bone using the diffusion-adsorption model

Abstract U-series dating of bone has suffered problems of reliability since its inception because bone remains an open system with respect to uranium. Commonly applied a priori assumptions of U uptake, such as early uptake or linear uptake, are inadequate because they have no physical or chemical bases, no means of demonstrating which model is suitable for a particular bone, and no intrinsic tests of reliability. Despite this and numerous examples of anomalous U-series dates, such assumptions are still routinely applied. We address this problem using the diffusion-adsorption (D-A) model of U uptake (Millard and Hedges, 1996), which incorporates a physicochemical description of U uptake. Using this model, we show how the U uptake of a bone responds to geochemical changes in the burial environment, which can lead to phenomena such as the removal of U from bones (“leaching”) or U uptake late in their burial history (“recent uptake”), and we show how the overall uptake history is reflected in distributions (profiles) of U and U-series isotopes across a bone section. We present measurements of U concentration profiles, and 230 Th/ 234 U profiles on archeological bone from a number of different sites and burial environments and compare the results to profiles predicted by the D-A model. Bones that have undergone complex uptake histories (which include U leaching or recent uptake) are identified on the basis of these profiles and rejected as unsuitable for dating. For bones that appear to have undergone uptake under constant geochemical conditions, the D-A model is applied to calculate U-series dates, with much improved reliability.

Ancient DNA Suggests a Recent Expansion of European Cattle from a Diverse Wild Progenitor Species

A total of 11 Bos primigenius and Bos taurus bones from archaeological sites between 500 and 12000 years old were examined for the presence of DNA. It was possible to amplify and sequence mitochondrial control region DNA extracted from seven of the 11 samples, including two Pleistocene B. primigenius samples. We compared the results with published data by constructing phylogenetic networks. The two B. primigenius samples clustered with the extant B. taurus samples in the networks. The similarity between B. primigenius and modern taurine cattle confirms that these should be considered members of a single species. The sequences obtained from the B. taurus specimens were either identical to the reference sequence for modern European cattle or closely related to it. They included two sequences not previously documented. The network analysis of the ancient data highlights the intermediary nature of the B. primigenius sequences between modern European and African B. taurus and the proximity of the ancient DNA B. taurus sequences to modern European B. taurus. Further analysis of the extant data in the light of the ancient DNA results suggests that a degree of Pleistocene diversity survives in the extant European Bos population that is mainly derived from a more recent population expansion.

HYBRID ION SOURCES: RADIOCARBON MEASUREMENTS FROM MICROGRAM TO MILLIGRAM

Abstract Gas ion sources provide a very efficient way of dealing with very small samples and, by injecting samples in a stream of helium carrier gas, measurements can be obtained from as little as 1 μg carbon. This is particularly useful for measurements on high activity samples and for the study of sample contaminants in relation to high precision AMS measurements. Another benefit of gas based measurements is that they can be made in real time allowing a range of possible applications such as GC-AMS and LC-AMS which could make AMS more widely applicable in the life sciences. Graphite ion sources provide a more efficient use of accelerator time for the measurement of large samples because of the higher carbon currents attainable. The precisions attainable is this way are so good that re-evaluation of possible sources of systematic error (such as low level contamination and sample size effects) is essential. Hybrid ion sources capable of operating on either gas or graphite allow the advantages of both techniques to be exploited. With minor modifications to the gas ion source at Oxford we are now able to operate with both sample types. Currents from gas are typically 10–12 μA and those from graphite 40–50 μA while maximum currents from graphite exceed 300 μA. We discuss the implications of this for the future development of radiocarbon AMS facilities designed for a wide variety measurements and research.